微波和常规烧结制备纳米Al_2O_3/3Y-TZP陶瓷

采用共沉淀法制备Al2O3/3Y-TZP纳米粉体,粉体压制后通过微波和常规烧结制备Al2O3/3Y-TZP陶瓷,并研究两种烧结方法对Al2O3/3Y-TZP陶瓷相对密度、抗弯强度、断裂韧性和断口形貌等的影响。结果表明,共沉淀法制得的Al2O3/3Y-TZP纳米粉体晶粒细小、均匀,近似球形,尺寸为40~60nm;随烧结温度的升高,两种烧结方法制备的陶瓷试样相对密度、抗弯强度和断裂韧性均先升高后降低;与常规烧结相比,Al2O3/3Y-TZP陶瓷的微波烧结温度明显降低,时间显著缩短,且晶粒更细小,相对密度、抗弯强度和断裂韧性显著提高。     

14mol?-TZP和Al_2O_3/Ce-TZP层状复合材料的研究

本文主要通过对含有14mol％CeO2的Ce－TZP及不同结构参数的Ce－TZP／Al2O3层状复合材料断裂韧性的测试，从力学和材料角度出发分析Al2O3层厚及Al2O3层中Ce－TZP的含量对材料力学性能的影响．同时通过对KIc试样断裂后断面及受力侧面的激光拉曼微区分析，来定性解释Al2O3层的引入对Ce－TZP相变区形状及相变量的影响，从而揭示此类材料的增韧机制．     

共沉淀法合成制备Ce^3＋掺杂Lu3Al5O12纳米粉体

用碳酸氢铵作为沉淀剂,将硝酸镥、硝酸铝和硝酸铈配成混合溶液,采用反滴定共沉淀及低温煅烧前驱体的方法制备 Lu3Al5O12(Ce)纳米发光粉体.采用热分析(TG-DTA)、傅立叶红外光谱(FTIR)、X射线衍射(XRD)、透射电镜(TEM)和光致发光(PL)等分析测试方法对Lu3Al5O12(Ce)粉体制备过程中的物理化学变化及粉体的激发发射发光性能进行了研究.结果表明,采用反滴定共沉淀法制备工艺,经过1000℃煅烧2h,可以得到晶粒尺寸为30nm左右,仅有轻微团聚,单一石榴石相的Lu3Al5O12(Ce)粉体.并且在1000℃处理得到的粉体的光致发光最强.     

SPS合成Al2O3-Al2TiO5复相陶瓷的组织性能及磨损行为

以两种Al2O3-TiO2复合粉体为原料经SPS烧结制备出Al2O3-Al2TiO5复相陶瓷.采用纳米结构复合粉体烧结而成的复相陶瓷有着较优的力学性能,特别是具有较高的断裂韧性和硬度,与其较小的晶粒尺寸相对应.干滑动摩擦磨损试验在4N和6N法向载荷下进行,结果表明,采用微米结构复合粉体烧结而成的复相陶瓷磨损表面较光滑,体积磨损量较小.在磨损试验中,纳米结构复合粉体烧结而成的复相陶瓷的破坏方式为沿晶断裂,有明显的晶粒拔出现象;微米结构复合粉体烧结而成的复相陶瓷呈不连续的微观断裂并产生塑性变形;同时,两种材料在摩擦磨损过程中都发生接触面的氧化和物质转移.     

常压烧结制备亚微米晶Al2O3陶瓷及其力学性能研究

以高纯α-Al2O3粉体为原料,MgO-Y2O3为烧结助剂,采用常压烧结法制备亚微米晶Al2O3陶瓷。研究了烧结温度、烧结助剂对Al2O3陶瓷的致密化过程、显微结构及力学性能的影响。结果表明:添加一定量的复合助剂MgO-Y2O3可起到促进Al2O3陶瓷致密化,细化显微结构,并改善其力学性能的作用。经1450℃常压烧结1h可获得相对密度达99.6%、平均晶粒尺寸约0.71μm的亚微米晶Al2O3陶瓷,其维氏硬度和断裂韧性分别为18.5GPa和4.6 MPa·m1/2。     

常压烧结制备亚微米晶Al2O3陶瓷及其力学性能研究

以高纯α-Al2O3粉体为原料,MgO-Y2O3为烧结助剂,采用常压烧结法制备亚微米晶Al2O3陶瓷。研究了烧结温度、烧结助剂对Al2O3陶瓷的致密化过程、显微结构及力学性能的影响。结果表明:添加一定量的复合助剂MgO-Y2O3可起到促进Al2O3陶瓷致密化,细化显微结构,并改善其力学性能的作用。经1450℃常压烧结1h可获得相对密度达99.6%、平均晶粒尺寸约0.71μm的亚微米晶Al2O3陶瓷,其维氏硬度和断裂韧性分别为18.5GPa和4.6 MPa·m1/2。     

亚微米ZrO_2粉体对氧化铝陶瓷力学性能的影响

在高纯Al2O3粉体中添加质量分数为16%的亚微米ZrO2粉体,制备Al2O3-ZrO2复合粉体,通过X射线衍射仪、电子探针和扫描电子显微镜分别对样品的相组成和显微结构进行分析,研究不同烧结温度下亚微米ZrO2粉体对氧化铝陶瓷抗折强度和硬度的影响。结果表明,在1 450℃时无压烧结2 h,Al2O3-ZrO2复相陶瓷的晶粒粒径约为0.5μm,抗弯强度高达797 MPa,提高了46%,维氏硬度为17.9 GPa。     

YAG-Al2O3纳米复合材料的制备和力学性能

本文介绍用化学共沉淀和在适当温度下煅烧以直接制备YAG-Al2 O3纳米复合粉体的新方法．XRD结果表明,所得粉体具纯的YAG和α-Al2 O3相,因此其化学组成符合配料的组分设计．用本方法制备的25vol％YAG-Al2 O3复合粉体经热压烧结,所得的致密体材料为晶内型纳米复合材料,其抗弯强度达612MPa,断裂韧性为4．54MPa．m-1/2,都比单相Al2 O 3陶瓷有大幅度提高．     

采用放电等离子烧结法制备ZrB_2-YAG-Al_2O_3复相陶瓷

ZrB2具有优良的物理特性和化学稳定性而应用于许多领域,但ZrB2难以烧结致密。通过共沉淀法获得包覆式Al2O3-Y2O3/ZrB2复合粉体并对其进行放电等离子烧结来提高ZrB2陶瓷的致密度。研究表明:包覆型粉体在700~1000℃时出现一次收缩,然后在1100℃之后出现第二次收缩。根据研究结果得出适宜制备高致密的ZrB2-YAG-Al2O3复相陶瓷的参数为:烧结温度为1700℃,烧结压力为20MPa,保温时间为4min,YAG-Al2O3的添加量为30wt%,用此参数可以成功制备出相对密度大于95%的ZrB2-YAG-Al2O3复相陶瓷,证明通过原料包覆的途径添加YAG-Al2O3可以促进ZrB2-YAG-Al2O3复相陶瓷的烧结致密化。     

高能球磨Al-Y203粉体固相反应制备YAG陶瓷的研究

用高纯Al粉体和Y2O3粉体(Al-Y2O3粉体)为原料采用固相反应法制备了YAG陶瓷. Al-Y2O3粉体高能经过球磨,煅烧生成YAG粉体,再真空烧结制备高致密YAG陶瓷.采用DTA-TG对球磨Al-Y2O3粉体进行分析,采用XRD、SEM对球磨的Al-Y2O3粉体、YAG粉体及YAG陶瓷进行了表征.实验表明:Al-Y2O3粉体在～569℃时,Al粉强烈氧化,并与Y2O3粉反应,600℃煅烧出现YAM相,随煅烧温度升高出现YAP相,1200℃煅烧生成YAG粉体.成型YAG素坯在1750℃保温2h真空烧结出YAG相陶瓷,YAG陶瓷相对密度可达98.6%,晶粒生长均匀,晶粒尺寸为8～10μm.     

R-curve behaviour of 9Ce-TZP zirconia ceramics

Stabilised zirconia ceramics may undergo a stress-induced tetragonal-to-monoclinic phase transformation. At crack tips, a transformation zone with compressive stresses develops, leading to an increase in fracture toughness, which depends on the size and geometry of the transformation zone. The influence of grain size on the R-curve behaviour and transformation zone size is investigated for five 9Ce-TZP zirconia ceramic materials of variable grain size.     

Toughness tailoring of yttria-doped zirconia ceramics

Despite the impressive development in understanding transformation toughening, tailoring the toughness of yttria-doped zirconia ceramics remained a major challenge. In our research, a simple but innovative route based on the mixing and hot pressing (under identical conditions) of zirconia powders with varying yttria content (3 and 0 mol%) is developed to investigate this critical issue. The experimental results clearly reveal that the fracture toughness of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics can be tailored by careful mixing of co-precipitated and yttria-free zirconia starting powders.     

Synthesis, microstructure and mechanical properties of ceria stabilized tetragonal zirconia prepared by spray drying technique

Ceria stabilized zirconia powders with ceria concentration varying from 6 to 16 mol% were synthesized using spray drying technique. Powders were characterized for their particle size distribution and specific surface area. The dense sintered ceramics fabricated using these powders were characterized for their microstructure, crystallite size and phase composition. The flexural strength, fracture toughness and microhardness of sintered ceramics were measured. High fracture toughness and flexural strength were obtained for sintered bodies with 12 mol% of CeO₂. Flexural strength and fracture toughness were dependent on CeO₂ concentration, crystallite size and phase composition of sintered bodies. Correlation of data has indicated that the transformable tetragonal phase is the key factor in controlling the fracture toughness and strength of ceramics. It has been demonstrated that the synthesis method is effective to prepare nanocrystalline tetragonal ceria stabilized zirconia powders with improved mechanical properties. Ce-ZrO₂ with 20 wt% alumina was also prepared with flexural strength, 1200 MPa and fracture toughness, 9.2 MPa√m.     

The effect of ceria co-doping on chemical stability and fracture toughness of Y-TZP

The fracture toughness and ageing resistance of yttria, ceria-stabilized tetragonal zirconia polycrystals (Y, Ce-TZP) were evaluated as a function of grain size and ceria content. Very fine grained, fully dense materials could be produced by sinter forging at relatively low temperatures (1150–1200 °C). The ageing resistance in hot water (185 °C) of 2 mol% Y₂O₃-stabilized TZP is strongly enhanced by alloying with ceria. The ceria content necessary to avoid degradation completely, decreases with grain size. The toughness of fully dense Y, Ce-TZP is 7–9 MPa m^1/2 for grain sizes down to 0.2 m. No or very little transformation took place during fracturing and no clear variation with grain size was observed for the toughness at grain sizes up to 0.8 m. Reversible transformation and crack deflection may explain the observed toughness values.     

Fracture variability and R-curve behavior in yttria-stabilized zirconia ceramics

An assessment of fracture origins is conducted in yttria-stabilized zirconia ceramics containing different grain sizes. As the microstructure coarsens due to the application of heat treatments, fracture origins change from single pores to transformed regions at the free surface which are induced by the applied stress. The observation of an increasing size of failure origins with microstructural coarsening lies as the underlying reason for the finding that specimens containing coarser microstructures and a more pronounced R-curve behavior do not fail at larger stresses. A fracture model is used to link the strength variability of a fully tetragonal zirconia containing a small grain size to its pore size distribution. The increased transformability of zirconia ceramics with coarser tetragonal grains is evaluated by means of quantitative phase analysis, characterizations of fracture surface morphology, and R-curve assessments. It is confirmed that tetragonal grains of up to 4 m may not necessarily undergo a spontaneous t–m transformation upon cooling from sintering.     

Sintering,microstructure and mechanical properties of commercial Y-TZPs

The sintering behaviour of Y-TZP ceramics, their resulting microstructures and properties are influenced not only by the characteristics of the raw materials but also were found to be dependent on the thermal history during the fabrication process. It is generally understood that fracture toughness increases as grain size increases up to a certain limit but in the present investigation, the results obtained challenge this view. The work is concerned with grain size dependence on the mechanical properties, in particular on the fracture toughness. Two commercially available powders based on two different processing techniques (i.e. coated and co-precipitated) were studied. It has been found that both materials exhibited different fracture toughness trends. Smaller grains of coated Y-TZP resulted in high fracture toughness >12 MPa m^1/2 while the opposite effect was seen in the co-precipitated material which showed enhanced fracture toughness with increasing grain size above a certain lower limit from a nonconventional heat treatment.     

低温烧结高性能2Y-TZP材料

通过在2Y-TZP中加入一定量的硅酸盐玻璃相添加剂,在较低的烧结温度下,制备出细晶、具有良好综合性能的2Y-TZP材料.研究了添加剂加入后,2Y-TZP材料烧结特性、显微结构及力学性能.发现加入少量的添加剂后,不但可以明显降低材料的烧结温度,而且由于细晶及相变增韧的共同作用,材料仍具有较高的抗折强度和断裂韧性.讨论了稳定剂含量对低温烧结Y-TZP力学性能的影响,发现较低稳定剂含量的2Y-TZP材料,由于临界相变尺寸小,在断裂过程中,有更多的四方相氧化锆转变成单斜相,相变增韧的效果更好,因而具有更高的断裂韧性.     

Pressureless sintered ATZ and ZTA ceramic composites

Alumina-20 wt% zirconia (ATZ) and zirconia-20 wt% alumina (ZTA) composites were prepared by conventional sintering of commercial powders, with average particle sizes in the range 0.35–0.70 m. Sintering at 1650 °C for 4 h resulted in final densities up to 96%. Bending strength and hardness increased with the final density. The tetragonal volume fraction was strongly dependent on both the final density and tetragonal grain size. The relatively high fracture toughness of 9 MPa m^1/2 was associated with the highly dense microstructure consisting of tetragonal grains of the critical size.     

Alumina versus Zirconia Comparative Survey of Thermic Influence During Dental Ceramic Core Manufacturing Process

For dental ceramic restorations, the manufacturing process presumes a high temperature sample heating treatment process, more than 1,000°C for applied aesthetic veneer and glazer. The present study presents and analyzes a comparative survey for two dental ceramics regarding the link between the heating treatment and reported cases of fractures and failure (delamination) of ceramic core. Two different dental ceramics samples were investigated: alumina based ceramic, respectively zirconia based ceramic materials. For zirconia based ceramic, changes concerning monoclinic (M) and tetragonal (T) crystalline phases occur and peak intensity variation from x-ray diffraction patterns are observed during heating process. For alumina based ceramic, the crystalline structure is less affected by the heating process but a different grain size and orientation were noticed during/after heating treatment. Both of them are affecting the strength and fracture toughness of the dental ceramic core.     

Thermal shock fracture behaviour of ZrO2 based ceramics

Thermal shock fracture behaviour of alumina, mullite, silicon carbide, silicon nitride and various kinds of zirconia based ceramics, such as magnesia partially stabilized zirconia (Mg-PSZ), yttria and ceria doped tetragonal zirconia polycrystals (Y-TZP and Ce-TZP), Y-TZP/Al₂O₃ composites and yttria doped cubic stabilized zirconia (Y-CSZ), was evaluated by the quenching method using water, methyl alcohol and glycerin as quenching media. Thermal shock fracture of all materials seemed to proceed by the thermal stress due to convective heat transfer accompanied by boiling of the solvents under the present experimental conditions. Thermal shock resistance of zirconia based ceramics increased with increasing the fracture strength, but that of Y-TZP and Y-TZP/Al₂O₃ composites was anormalously lower than the predicted value.